1. Field of the Invention
The present invention relates to spray guns for paint and other the liquids and particularly to airless or hydrostatic atomization types of spray guns.
2. Description of the Prior Art
Typical spray guns of the airless or hydrostatic type, as exemplified by U.S. Pat. No. 4,245,784, eject the fluid through at least one central channel of a discharge nozzle where the fluid is atomized into particles which are sprayed in a conical or fan shaped pattern. In some spray guns the fluid passageway or passageways are directed tangentially into a circular chamber situated immediately upstream of the discharge nozzle to impose a circular or whirling motion around the discharge axis of the spray pattern. In other spray guns the fluid is electrostatically charged at the time the spray pattern is established, as seen in additional prior art references, Canadian patent Nos. 965,943 of Patrick D. Shaffer and 972,949 assigned to Graco, Inc.
A typical airless spray gun has a pistol grip handle including a trigger and valve for controlling liquid flow and an adjustment element for varying the spray patterns and/or the degree of atomization. Such a spray gun has a principal fluid flow passage leading to the discharge nozzle, with a needle valve stem situated centrally in this passage and terminating in a ball or other valve closure element that engages a valve seat. A helical coil spring is situated within this fluid flow passage and surrounding the valve stem for biasing the valve to a closed position unless and until it is opened by the trigger.
Additional prior art references illustrating various spray guns include U.S. Pat. No. 4,572,438 to Traylor, U.S. Pat. No. 4,713,257 to Luttermoller, U.S. Pat. No. 4,750,676 to Huber, et al., U.S. Pat. No. 5,725,161 to Hartle, and U.S. Pat. No. 5,803,372 to Weinstein, et al.
While spray guns of these types are well known and relatively successful, they have various drawbacks as follows. Firstly, the spring and needle valve stem reside in the fluid flow passage where paint particles of the flowing fluid can dry and jam the apparatus or later become dislodged and bleed into subsequently used paint of a different color, or flake off and clog the discharge nozzle. Secondly, the basic or typical airless spray gun has a considerable number of components in a relatively complex assembly, such that it is quite difficult and time consuming for users to maintain and/or disassemble and repair the apparatus.